Contact bump construction for the production of a connector construction for substrate connecting surfaces

ABSTRACT

Contact bump construction ( 27 ) and method for the production of a contact bump construction for the formation of elevated contact sites on connecting surfaces ( 22 ) of a substrate ( 21 ), particularly chip connecting surfaces, with a spacer metallization ( 28 ) for the attainment of a defined height of the contact bump construction, wherein the spacer metallization ( 28 ) consists at least partly of annealed copper.

[0001] The invention relates to a contact bump construction for theformation of elevated contact sites on connecting surfaces of asubstrate, particularly chip connecting surfaces, in accordance with thepreamble of claims 1 and 10, and a bonding configuration betweenconnecting surfaces of substrates contacted by the use of the bumpconstruction in accordance with claims 4 and 18.

[0002] Particularly for producing contacts between chips in the“flip-chip” method, and for producing contacts on relatively large areasubstrates having a connecting surface distribution frequently realizedas an area array, for example a ball grid array, a direct contactingmethod has gained general acceptance in which elevated contactmetallizations, known by the technical term “bumps ”, are used to createa bond of opposing connecting surfaces of substrates that are to bebrought into contact with each other. As the density of such connectingsurfaces increases, the requirements also become more stringent for amethod of compensating tolerance that compensates both for thepositional deviations of the mutually assigned connecting surfaces ofthe substrates and also height differences of the bumps forming thecontacts, in order to prevent faulty contact or to minimize as far aspossible the mechanical stresses in the electronic components thatimpair the operating reliability of the components.

[0003] The object of this invention, therefore, is to suggest a bumpconstruction that enables tolerance compensation with respect to heightdifferences of the bumps and positional deviations of the connectingsurfaces that are to be brought into contact with each other.

[0004] This object is achieved by a bump configuration having thecharacteristics of claim 1.

[0005] In accordance with the first solution described above of theobject underlying the invention, the bump construction according to theinvention is furnished with a spacer metallization that consists atleast in part of annealed copper, provided on the connecting surfaces ofthe substrate in order to reach a defined height of the bumpconfiguration.

[0006] Within the terms of the solution according to the invention, abump construction is thus provided having a metallic structure made fromcopper, wherein the copper structure has a relatively coarse“re-crystallization structure” as a consequence of annealing, i.e. heattreatment, which overall lends flexibility to the bump constructionunder compression loading. In this way, even a multiplicity of bumpsarranged in distributed manner on a contact side of a substrate, andhaving varying heights in their original condition due to theunavoidable height tolerance intrinsic to a manufacturing process,caused by contact pressure upon contacting with another substrate, maybe compressed together to a uniform dimension. Thus it is possible inlarge measure to preclude faulty contact sites due to differing contactheights of individual bumps or component tensions arising from thecontacting process.

[0007] For the case of inadequate adhesion due to material pairingbetween the spacer metallization made from copper and the connectingsurface metallization of the substrate, an intermediate metallizationmay be provided for the indirect bonding of the spacer metallization tothe connecting surface. This is then especially advantageous if theintermediate metallization, unlike the spacer metallization, is not madefrom copper, but from aluminum for example. For the intermediatemetallization, the use of a Ni—Au layer construction on the connectingsurface metallization or the deposit of a Ni/Au alloy on the connectingsurface metallization has been proven to be advantageous.

[0008] It is especially advantageous if the intermediate metallizationor also the spacer metallization is an electroless deposit. The resultof electroless copper deposition with subsequent annealing is aplasticly deformable bump, free of internal stresses, “low stresselectroless bump”.

[0009] In order to increase reliability using the bump configurationaccording to the invention, it has proven to be advantageous if thespacer metallization is provided with a coating serving as an oxidationbarrier. Such a coating may be for example a Ni/Au, Sn, or Sn/Pb alloy.

[0010] A bonding configuration between connecting surfaces of mutuallycontacted substrates that is selected using the bump constructionaccording to the invention has a spacer metallization arranged on aconnecting surface of a first substrate which consists at least in partof annealed copper.

[0011] The bonding configuration may be produced with known thermalcompression procedures, for example, or also bonding techniquesparticularly with a non-conductive adhesive, i.e. techniques in which itis not absolutely necessary to employ an additional bonding substance.

[0012] However, it is also possible to provide a bonding substancebetween the spacer metallization and an assigned connecting surface of asecond substrate.

[0013] According to a particularly preferred embodiment, the bondingsubstance that is used in the production of a substance-enclosing,electrically conductive bond between the spacer metallization arrangedon the connecting surface of the first substrate and the assignedconnecting surface of the second substrate, consists of an anisotropicbonding material. The combination of the anisotropic adhesive materialas bonding substance with the spacer metallization made from annealedcopper enables—particularly because of the relatively good plasticdeformability of the annealed copper—the particular advantage of acontacting of the two substrates without significant thermal stress andconsequently without any possible effect on the crystallizationstructure of the spacer metallization. Moreover, the desired leveling ofthe heights of the spacer metallizations for a multiplicity of bumpsarranged in a shared contact plane takes place simultaneously with thecompressive load necessary for the production of a conductive contact.

[0014] In all cases, however, the bonding configuration according to theinvention also allows the use of a soldering material as bondingsubstance.

[0015] As was indicated previously with reference to the contact bumpconstruction according to the invention, corresponding advantages alsobecome evident for the bonding configuration with the arrangement of anoxidation barrier on the spacer metallization and/or arrangement of anintermediate metallization for indirect bonding of the spacermetallization to the connecting surface.

[0016] In the method for the production of a contact bump constructionaccording to the invention on connecting surfaces of substrates, inwhich copper is deposited by electroless means on the connectingsurfaces or on an intermediate metallization arranged on the connectingsurfaces to form a spacer metallization, the terms of the inventionprovide for a process step carried out following the deposition processin which the deposited copper is re-crystallized by exposure to heat toa temperature above the temperature of the deposition process.

[0017] With the subsequent heat treatment of the copper previouslydeposited by electroless means for example at a temperature ofapproximately 60° C., the copper is re-crystallized at a temperaturepreferably >100° C. This conversion of a structure that is somewhatamorphous due to the deposition process into a comparatively coarselycrystalline structure causes a reduction in hardness of the copperstructure with a consequential increase in the plastic deformability ofthe copper.

[0018] According to a further solution of the task underlying theinvention, a contact bump construction is suggested for the formation ofelevated contact sites on connecting surfaces of a substrate inaccordance with claim 10, which has a spacer body made from adielectric, whose at least partially electrically conductive surface isconnected to the assigned connecting surface of the substrate via anelectrical conductor, wherein the conductor is conformed at least partlyas a surface conductor arranged on the surface of the spacer body.

[0019] The combination according to the invention of non-conductivespacer body and surface conductor for the electrically conductivecontacting of the surface of the spacer body with the connecting surfaceof the substrate allows the connecting surfaces to be re-distributedand/or enlarged very simply without the formerly usual multi-layerconstruction layering on the contact side of a substrate.

[0020] With the bump construction according to the invention, deviationsin the regular surface-distribution of the connecting surfaces, known as“pitch errors”, may be compensated so that a reliable contact betweensubstrates is possible even if such deviations are present.

[0021] If the spacer body is arranged in a covering position relative tothe assigned connecting surface, an electrically conductive contactsurface of the spacer body with electrically conductive bonding to theconnecting surface of the substrate may be created by means of a partialformation of the conductor as a through-hole contact, which extendsthrough a hole in the spacer body.

[0022] According to a further embodiment, the spacer body may also bearranged with the conductor interposed on the connecting surface, andthe conductor may extend around at least a part of the perimeter of thespacer body as far as the top side of the spacer body.

[0023] If the spacer body is arranged with a partial area on a firstpartial surface of the connecting surface and moreover extends beyondthe connecting surface, while the conductor of a second partial surfaceof the connecting surface extends as far as the top surface of thespacer body, a re-bonding or re-distribution of the effective connectingsurfaces, may be realized in particularly simple manner.

[0024] In order to achieve a connection that is permanently electricallyreliable between the connecting surface and the electrically conductiveupper side of the non-conductive spacer body, it has proven advantageousif the conductor at least in the areas beyond the connecting surface isfurnished with a bonding agent layer as a carrier for a contactmetallization of the conductor.

[0025] Such a bonding agent layer may be formed for example if thecorresponding surface areas of the electrically non-conductive surface,that is to say for example the chip passivation, is seeded withpalladium so that on the one hand deposition onto non-metallic surfacesis also possible by reason of the low selectivity of palladium, and onthe other hand deposited palladium particles may be used as seeds for asubsequent metal deposition of copper or a Cu/Ni-alloy for example.

[0026] In order to strengthen the adhesion between the conductor and theconnecting surface and/or the surface of the spacer body, the connectingsurface may be provided with a contact metallization containing Ni andAu.

[0027] A bonding configuration produced with the use of the contact bumpconstruction according to the invention between connecting surfaces ofcontacted substrates has in accordance with the invention a spacer bodyarranged on a connecting surface of a first substrate to achieve adefined height of the bonding configuration, and a bonding substancearranged between the spacer body and an assigned connecting surface of asecond substrate, wherein the spacer body consists of a dielectric,whose at least partly electrically conductive surface is connected withthe connecting surface of the first substrate via an electricalconductor.

[0028] Depending on the form taken by the spacer bodies, the bondingconfiguration according to the invention not only enables compensationof pitch errors in a bond between two substrates, but also a relativeenlargement of the connecting surfaces and/or re-distribution of theconnecting surfaces.

[0029] Particularly the enlargement of the connecting surfaces thusenabled makes possible a preferred use of an anisotropic adhesivematerial as a bonding substance.

[0030] In the following, preferred embodiments of a contact bumpconstruction and bonding configurations created using such contact bumpconstructions are explained in detail with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 shows a first embodiment of a contact bump constructionwith intermediate metallization;

[0032]FIG. 2 shows a second embodiment of a contact bump constructionwithout intermediate metallization;

[0033]FIG. 3 shows a bonding configuration between two substrates usingthe contact bump construction represented in FIG. 2;

[0034]FIG. 4 shows an enlarged detail of a bonding configuration;

[0035]FIG. 5 shows a connecting surface area of a substrate withintermediate metallization and surface-conductor layer;

[0036]FIG. 6 shows the connecting surface area of FIG. 4 with adielectric enclosing layer;

[0037]FIG. 7 shows the connecting surface area of FIG. 5 with a spacerbody formed from a dielectric;

[0038]FIG. 8 shows the connecting surface area of FIG. 6 with anotherembodiment of a contact bump construction;

[0039]FIG. 9 shows a further embodiment of a contact bump constructionwith spacer body;

[0040]FIG. 10 shows a bonding configuration created using a furtherembodiment of a contact bump construction with spacer body between twosubstrates;

[0041]FIG. 11 shows a corner area of a substrate furnished with aplurality of contact bump constructions corresponding to FIG. 8;

[0042]FIG. 12 shows a corner area of a substrate furnished with aplurality of contact bump constructions corresponding to FIG. 9.

[0043]FIG. 1 shows a connecting surface area 20 of a substrate 21 within the present case a connecting surface 22 made from aluminum that isfurnished with a two-layer intermediate metallization 23 including alayer of nickel 24 and a layer of gold 25. With the exception of theconnecting surface area 20, the substrate 21, for example a chip, isprovided with a so-called “passivation” 26.

[0044] In the embodiment shown in FIG. 1 in order to create a contactbump construction 27 on the connecting surface 22, the intermediatemetallization 23 is furnished with a spacer metallization 28 made fromcopper. On its surface, the spacer metallization 28 is furnished with acoating 29 which may be made for example from gold, a nickel/gold alloy,tin or a tin/lead alloy to prevent surface oxidation. The coating 29 mayserve particularly to smooth micro-roughnesses on the surface of spacermetallization 28.

[0045] As indicated in FIG. 1, the spacer metallization 28 made fromcopper has a relatively coarse, crystalline grain structure, which isthe result of a heat treatment following arrangement of the spacermetallization 28 on the intermediate metallization 23. In order toarrange the spacer metallization 28, copper is deposited by electrolessmeans on the intermediate metallization 23 following electrolessdeposition of nickel and gold on the connecting surface 22 to form theintermediate metallization 23. Nickel and gold are deposited to achievelayer thicknesses for example from 5 to 20 micrometres and from 0.1 to0.5 micrometres respectively. In particular the chemical process ofcopper deposition is performed at a temperature below 100° C., forexample about 60° C. The result of the electroless deposition process isa copper layer having a practically amorphous structure. By subsequentheat treatment at a temperature >100° C. the copper structure isre-crystallized with a comparatively coarse, crystalline structure as aresult, which presents evident hardness reduction compared with theinitial structure.

[0046]FIG. 2 shows a contact bump construction 33 formed on a connectingsurface 31 of a substrate 32, in which the spacer metallization 28 isapplied directly, that is without intermediate metallization 23, to theconnecting surface 31 by electroless copper deposition.

[0047]FIG. 3 shows a bonding configuration 34 between two substrates 32and 35 using contact bump constructions 33, as shown in FIG. 2. In orderto create the contact shown in FIG. 3 the substrate 35 assigned withconnecting surfaces 36 is first provided, and the connecting surfaces 36are furnished with a bonding substance of anisotropic adhesive 37.

[0048] The substrate 32 provided with contact bump constructions 33 iscontacted by the “flip-chip” technique, wherein the substrate 32 withcontact bump constructions 33 aligned towards the connecting surfaces 36of the substrate 35 is brought into contact with the connecting surfaces36 and pressed against them with a defined compressive force.

[0049] This creates an electrically conductive contact of the contactbump constructions 33 with the connecting surfaces 36 through theconductive particles arranged in the anisotropic adhesive 37, and aplastic deformation of the spacer metallizations 28 of the contact bumpconstructions 33 takes place such that the different heights h₁ to h₄ ofthe contact bump constructions 33 in the originally unloaded condition(dashed line) are deformed until a uniform height H of the bumpconstructions 33 is achieved. Consequently, from all the bondingconfigurations formed between the substrates 32 and 35, there is createda reliable mechanical and electrical contact having uniform contactheight, with an arrangement of the substrates 32 and 35 that isessentially parallel and free from body stresses.

[0050] The plastic deformation of the spacer metallizations 28 duringflip-chip contacting also enables the surface contour of the spacermetallizations 28 to be conformed to the surface contour of theconnecting surfaces 36, as shown in exemplary manner in FIG. 4. Theextensive surface contact made possible hereby is particularlyadvantageous in conjunction with bonding techniques in which no bondingmaterial is used between the contact partners to even out the deviationsin the surface contours of the contact partners, such as for example inthe thermal compression method or a compound with non-conductiveadhesive, in which the adhesive is essentially arranged on the peripheryof the bonding configuration.

[0051] FIGS. 5 to 8 thereafter show the production of a contact bumpconstruction 38 in the connecting surface area 39 of a substrate 40.

[0052]FIG. 5 shows the connecting surface area 39 having a connectingsurface 41 and a surface of the substrate 40 insulated by a passivation42, with exception of the connecting surface surface 41. In the presentcase, the connecting surface 41 is made from aluminum and is furnishedwith an intermediate metallization 23 including a layer of nickel 24 anda layer of gold 25. The entire connecting surface area 39 is coveredwith a surface conductor layer 43 as surface conductor, which in thepresent case has a contact metallization consisting of acopper/nickel-alloy on a carrier preferably containing palladium. Ifrequired, the carrier may serve to assure the desired adhesion betweenthe contact metallization of the surface conductor layer 43 and anon-metallic base, which is to say the passivation 42.

[0053]FIG. 6 shows an electrically non-conductive thick layer 44 made ofa dielectric on the connecting surface area 39 and a photo-mask 45arranged on the thick layer 44, enabling a spacer body 46 to beconformed in an etching procedure or similar out of the thick layer 44.

[0054] As is shown in FIG. 7, an etching procedure may be used tostructure the spacer body 46 and at the same time remove the surfaceconductor layer 43 in the area surrounding the spacer body 46.

[0055] Finally, FIG. 8 shows the completed contact bump construction 38with a surface conductor layer 43 extending beyond the outer peripheryof the spacer body 46, and thereby bonding an upper side 47 of thespacer body 46 in electrically conductive manner with the connectingsurface 41.

[0056] In the embodiments of the contact bump constructions shown inFIG. 8 and also in FIGS. 9 and 10, the connecting surfaces are made fromaluminum, so that an intermediate metallization of the type describedpreviously is practical for further contacting of the connectingsurfaces. In the event that the connecting surfaces are made fromcopper, of course it is possible to make a contact without intermediatemetallization.

[0057] In a further embodiment, FIG. 9 shows a contact bump construction48 having a spacer body 49 that is arranged in a covering position witha connecting surface 50 of a substrate 51 and is furnished with athrough-hole 52. The spacer body 49 is furnished with a surfaceconductor layer 43 both on its underside 53 and on its upper side 54,which permits an electrically conductive connection from the upper side54 to the underside 53 through a hole wall 55 of the through-hole 52 andto the connecting surface 50 via the intermediate metallization 23.

[0058] In a different approach to that shown in FIG. 9, it is alsopossible to dispense with the arrangement of the surface conductor layer43 on the upper side 54 of the spacer body 49, and to create a directbonding configuration by using a suitable bonding substance to establisha direct contact with the surface conductor layer 43 arranged on theunderside 53 or the intermediate metallization 23.

[0059]FIG. 10 shows a bonding configuration 56 between two substrates 57and 58 using a further embodiment of a contact bump construction 59. Thecontact bump construction 59 includes a spacer body 60, which is locatedwith a partial left area 61 in a overlapping position with a partialarea 79 of a connecting surface 62 of the substrate 57. In the presentcase, the connecting surface 62 is made from aluminum and is furnishedwith an intermediate metallization 23 including a layer of nickel 24 anda layer of gold 25. In order to create an electrically conductive bondbetween an upper side 63 of the spacer body 60 and a second partial area80 of the connecting surface 62, via the intermediate metallization 23,a surface conductor layer 65 extends from the upper side 63 over aperipheral area 64 of the spacer body 60 and over the intermediatemetallization 23.

[0060] An anisotropic adhesive 67 is provided as bonding substance toassure a contact between the upper side 63 of the spacer body 60furnished with the surface conductor layer 65, and a connecting surface66 of the substrate 58.

[0061] From the representation of the bonding configuration 56 betweenthe substrates 57 and 58 it is evident that with the contact bumpconstruction 59 including the spacer body 60 it is possible tore-distribute or re-wire the contact surface structure of the substrate57 so that it may be adapted to the contact surface structure or contactsurface distribution of substrate 58.

[0062]FIG. 11, which shows a plan view of a corner area of a substrate68, whose connecting surfaces 69 are furnished with contact bumpconstructions 73, 74, 75 with spacer bodies 70, 71 and 72, clearlyreveals that, depending on the selection of their geometry, the spacerbodies 70, 71, 72 allow considerable enlargement of the contact surfacearea because of the size of their contact upper sides 76, 77, 78, whichare considerably larger than the contact surfaces 69. In the presentcase, the contact bump constructions 73, 74, 75 may be conformed forexample according to the type of contact bump construction 38represented in FIG. 8.

[0063] By varying the geometry of the individual spacer bodies 70, 71,72, it is possible to produce contact upper sides 76, 77, 78 havingvarious surface shapes with corresponding surface areas. Contactsurfaces that are enlarged in this way allow not only re-bonding andadaptation to a contact surface distribution of a counter substrate (notshown in FIG. 10) but also, because of the larger contact areas,compensation of intrinsic tolerance deviations in the contact surfacedistribution between the substrate and counter substrate. In addition,the enlarged contact areas of the contact upper sides 76, 77, 78 form anespecially secure basis for the bonding configurations betweensubstrates that are contacted with the adhesive.

[0064]FIG. 12, shows a plan view of a corner area of a substrate 81whose connecting surfaces 82, unlike the substrate 68 with contact bumpconstructions 83, 84 in FIG. 11, are furnished with a contact bumpconstruction 48 similar to the type shown in FIG. 9.

I claim:
 1. A contact bump construction for the formation of elevatedcontact sites on connecting surfaces of a substrate, particularly chipconnecting surfaces, having a spacer metallization to achieve a definedheight of the contact bump construction, characterized in that thespacer metallization (28) consists at least in part of annealed copper.2. The contact bump construction according to claim 1, characterized inthatan intermediate metallization (23) is provided for the indirectconnection of the spacer metallization (28) with the connecting surface(41).
 3. The contact bump construction according to claims 1 or 2,characterized in that the spacer metallization (28) is provided with acoating (29) serving as an oxidation barrier.
 4. A bonding configurationbetween connecting surfaces of mutually contacted substrates having aspacer metallization arranged on a connecting surface of a firstsubstrate to achieve a defined height of the bonding configuration,characterized in that the spacer metallization (28) consists at least inpart of annealed copper.
 5. The bonding configuration according to claim4, characterized in that a bonding substance is arranged between thespacer metallization (28) and an assigned connecting surface (36) of asecond substrate.
 6. The bonding configuration according to claim 5,characterized in that the bonding substance consists of an anisotropicadhesive (37).
 7. The bonding configuration according to claim 5,characterized in that that the bonding substance consists of solderingmaterial.
 8. The bonding configuration according to one or more ofclaims 4 to 7, characterized in that the spacer metallization (28) isfurnished with a coating (29) functioning as an oxidation barrier. 9.The bonding configuration according to one or more of claims 4 to 8,characterized in that an intermediate metallization (23) is provided forthe indirect connection of the spacer metallization (28) with theconnecting surface (41).
 10. A method for the creation of a contact bumpconstruction on connecting surfaces of substrates, particularly chipconnecting surfaces, wherein copper is deposited in electroless manneron the connecting surfaces or on an intermediate metallization arrangedon the connecting surfaces for the formation of a spacer metallization,characterized in that in a process step following the deposition processthe deposited copper is re-crystallized by thermal loading with atemperature above the temperature of the deposition process.
 11. Thecontact bump construction for the formation of elevated contact sites onconnecting surfaces of a substrate, particularly chip connectingsurfaces, with a spacer body, whose at least partly electricallyconductive surface is connected to the assigned connecting surface ofthe substrate through an electrical conductor, characterized in that thespacer body (46, 49, 60, 70, 71, 72) is constructed from a dielectric,and the conductor is conformed at least partly as a surface conductor(43, 65) arranged on the surface of the spacer body.
 12. The contactbump construction according to claim 11, characterized in that thespacer body (49) is furnished with a through-hole (52) that is arrangedin a covering position with the connecting surface (50), and the surfaceconductor (43) is partly conformed as a through-hole contact.
 13. Thecontact bump construction according to claim 11, characterized in thatthe spacer body (46) is arranged on the connecting surface (41) withintermediate arrangement of the surface conductor (43), and the surfaceconductor extends at least partly around the perimeter of the spacerbody as far as an upper side (47) of the spacer body.
 14. The contactbump construction according to claim 11, characterized in that thespacer body (60) is arranged with a partial area (61) on a first partialsurface (79) of the connecting surface (62) and also extends beyond theconnecting surface, and the surface conductor (65) extends from a secondpartial area (80) of the connecting surface to an upper side (63) of thespacer body.
 15. The contact bump construction according to one or moreof claims 11 to 14, characterized in that the surface-conductor (43, 65)has at least in the areas beyond the connecting surface (41, 50, 62, 69)an adhesion agent layer as a carrier for a contact metallization of theconductor.
 16. The contact bump construction according to claim 15,characterized in thatthe adhesion agent layer includes palladium. 17.The contact bump construction according to claim 15 or 16, characterizedin that the contact metallization includes copper or a Cu/Ni alloy. 18.The contact bump construction according to one or more of claims 11 to17, characterized in that the connecting surface (41, 50, 62, 69) and/orthe surface of the spacer body (46, 49, 60, 70, 71, 72) is furnishedwith a contact metallization (23) containing Ni and Au.
 19. The bondingconfiguration between connecting surfaces of mutually contactedsubstrates with a spacer body arranged on a connecting surface of afirst substrate for the achievement of a defined height of the bondingconfiguration and a bonding substance arranged between the spacer bodyand an assigned connecting surface of a second substrate, characterizedin that, the spacer body (46, 49, 60, 70, 71, 72) consists of adielectric whose at least partly electrically conductive surface isconnected with the connecting surface (41, 50, 62, 69) of the firstsubstrate through an electrical surface conductor(43, 65).
 20. Thebonding configuration according to claim 19, characterized in that thebonding substance consists of an anisotropic adhesive (67).